1 . Field of the Invention
The present invention relates to a control system for executing an automatic stop control of an engine when predetermined engine stop conditions are satisfied during the running of a vehicle.
2. Related Art
In recent years, a vehicle having an internal combustion engine such as a gasoline engine mounted thereon is more and more demanded to reduce emissions and improve a fuel economy. In order to satisfy these demands: reductions have been made in the weight of a body; technical improvements have been made for lean-burning; and techniques have been developed for stopping the feed of a fuel in accordance with running states. Of these techniques, one is a fuel feed stop control (or a fuel-cut control) at a deceleration. This is a control for suppressing a fuel consumption at the deceleration with a fully closed throttle by interrupting the fuel feed to the engine in the state where the engine speed is within such a range of a predetermined number of revolutions per minute as enables the restart of the engine by reopening the fuel feed.
In this fuel-cut control, the rotation of the engine is kept by transmitting the running inertia force of the vehicle to the engine, and the engine is cranked up for a restart by the running inertia force of the vehicle. This limits the vehicle speed capable of executing the fuel-cut control to a higher value than the vehicle speed necessary for restarting the engine thereby to restrict the effect for improving the fuel economy.
On the other hand, the so-called xe2x80x9cECO-run controlxe2x80x9d is known, as another example for improving the fuel economy, to have the meaning of the xe2x80x9cECOnomical-ECOlogical runxe2x80x9d. This is the technique for suppressing the fuel consumption by stopping the fuel feed and the ignition, when it is satisfied as stop conditions that an air conditioner stops, and that a rightward turn signal is OFF in addition to the first condition that the vehicle stops. In this ECO-run control, the engine is cranked up and restarted by a starter or a motor-generator so that the engine can be stopped when the vehicle stops.
Since the ECO-run control is conditioned at first by the stop of the vehicle, however, it is not executed in a decelerating state where the vehicle speed is lower than the speed range in the aforementioned fuel-cut control and where the vehicle is just about to stop, so that the fuel is fed although no driving force is especially needed. In the vehicle for executing both the fuel-cut control and the ECO-run control, therefore, the fuel feed is stopped in the state where the vehicle speed is in a fuel-cut region, when the vehicle is decelerated from a predetermined speed to stop. As the vehicle speed becomes lower than the fuel-cut region, the fuel feed is then reopened. When the vehicle stops, moreover, the fuel feed is stopped again. Thus, the fuel is unnecessarily consumed between the fuel-cut control and the ECO-run control.
In Japanese Patent Laid-Open No. 8-14076 (JP-A-8-14076), there is disclosed a technique in which the fuel feed and the ignition are interrupted to stop the engine automatically when predetermined stop conditions are satisfied by the vehicle speed of substantially zero and by the parking brake ON. An additional disclosure is that when the fuel-cut control is executed prior to the automatic engine stop control at a vehicle stop, the engine stop state by the fuel-cut may be continued till the vehicle stops. However, since the fuel-cut control is executed on the premise that the engine is restarted by cranking up the engine with the running inertia force of the vehicle, as described above, it cannot be continued till the vehicle speed becomes lower than the restartable speed and the vehicle stops.
In the prior art, Japanese Patent Laid-Open No. 7-266932 (JP-A-7266932) has, proposed a control for improving the fuel economy by stopping the engine during a deceleration at a lower vehicle speed than the fuel-cut region. In the control system disclosed, the automatic stop control of the engine is executed in a predetermined deceleration state where a demanded torque is lower than the running resistance. When the state where the change in the vehicle speed is within a predetermined region (e.g., 25 Km/hour or more) for a predetermined deceleration and where the throttle opening is less than a set value (e.g., an opening corresponding to a decelerating vehicle speed) continues for a predetermined time period (e.g., about 1 sec.), the fuel injection is stopped assuming that the automatic engine stop condition is satisfied. Immediately after this (e.g., after 0.5 secs.), moreover, the clutch is released to stop the rotation of the engine completely.
In the invention disclosed in Japanese Patent Laid-Open No. 7-266932, the engine is automatically stopped during a gentle deceleration just before the vehicle stops, so that the fuel consumption can be reduced in the decelerating state between the fuel-cut control and the so-called xe2x80x9cECO-run controlxe2x80x9d to improve the fuel economy accordingly. In the invention disclosed in Japanese Patent Laid-Open No. 7-266932, on the other hand, a starting clutch is released to stop the rotation of the engine completely in accordance with the automatic stop control of the engine during the gentle deceleration, so that no vacuum is established in the engine. When the automatic engine stop control is to be executed during the deceleration, therefore, the vacuum of a brake system is retained by a motor-driven vacuum pump.
If this motor-driven vacuum pump is provided for executing the automatic stop control of the engine during the deceleration, however, an accessory for the vehicle is added to increase the weight of the body. As a result, the fuel economy of the vehicle is adversely affected to go against the intrinsic object to execute the automatic stop control of the engine. On the other hand, the provision of the vacuum pump raises a load on the battery. When the state of charge (SOC) of the battery is low, the vacuum pump may not be sufficiently driven to lower the braking force or the braking operability. In a vehicle having a power steering mechanism mounted thereon, moreover, the rotation of the engine is completely stopped during the deceleration. As a result, the hydraulic pump of the power steering mechanism may not be driven to fail to establish the oil pressure necessary for the steering operations.
An object of the invention is to provide a control system capable of stopping an engine automatically at a deceleration to improve the fuel economy while preventing a reduction in a drivability of a vehicle.
An example of this drivability is a braking operability, by which an event that demands a high brake pedal depression can be avoided in advance according to the invention even if the fuel feed to the engine is stopped. Another example of the drivability is a steering operability, by which an event that demands a high steering force can be avoided in advance according to the invention even if the fuel feed to the engine is stopped.
Specifically, the invention is intended to cover a vehicle equipped with an action mechanism which has an action content influenced by the rotating state of the engine. This action mechanism is exemplified by: a brake booster which can hardly establish the vacuum as the engine rotation lowers; and an oil pump which establishes a lower oil pressure as the engine rotation lowers.
The fuel feed to the engine during the running can be stopped only when no engine output is demanded. In the invention, therefore, it is decided whether or not the vehicle is coasted by the deceleration and whether or not the engine is rotated by the running inertia force owned by the vehicle. While the engine is forced to rotate by the torque transmitted from wheels, the action content of the action mechanism accords with the rotating state of the engine forced to rotate. It is decided whether or not the action content is sufficient for intrinsic functions of the action mechanism and for the running state of the vehicle. If the action content of the action mechanism is insufficient at the decision time, the stop of the fuel feed to the engine is inhibited. In other words, the fuel is continuously fed to the engine to keep it in a driving state. This prevents the action content of the action mechanism from becoming short.
If the action content of the action mechanism is sufficient, on the contrary, the fuel feed to the engine is stopped. With this sufficient action content of the action mechanism, therefore, the drivability of the vehicle is not deteriorated while improving the fuel economy.
In the invention, on the other hand, the control to stop the engine automatically at a deceleration can be executed on the basis of the selecting operation of the driver. If the fuel feed to the engine is stopped during a deceleration at a low speed to force the engine to rotate by the running inertia force owned by the vehicle, the engine rotation may become unstable and vibratory to cause the vehicle behaviors which would not occur in ordinary situations. If the driver selects controls against such behaviors by his own operations, however, the extraordinary vehicle behaviors such as the vibrations will not cause the driver to have a physical disorder.
The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read with reference to the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustrations only and are not intended as a definition of the limits of the invention.